A religion is a set of beliefs that is held by a group of people. There are many different religions, each with a different set of beliefs. The beliefs are about the world and the people in it, about how they came into being, and what their purpose is.
Each religion usually has their own type of "devotions" when people worship or pray. They often have religious "rituals" (special things that are always done in the same way) for certain times of the year or certain times of a person's life. Other words that are used for "religion" are "faith" and "belief system".You can read more about Christianity, Islam and Buddhism.
PS: This is a sample site from Digital Inspiration hosted on GAE. For any help, see the accompanying App Engine Tutorial.